Rubber-vulcanization accelerator



Patented CLAYTON QLIN NORTH, OF TALLMLADGE TOWNSHIP, SUMMIT COUNTY,OHIO, ASSIGNOB TO THE RUBBER SERVICE LABORATORIES 00., E

OHIO.

Ho Drawing.

My present invention relates to the art of vulcanizing rubber, andparticularly to the process of accelerating the vulcanization of therubber by employing a mixture of certain accelerators as hereinafter setforth, whereby a vulcanized rubber product of high quality andpossessing desirable commercial characteristics is obtained.

In my Patent 1,467,984, issued Septemher 11, 1923, I have claimed as anaccelerator of the rubber vulcanizing process, a compound produced bythe interaction of two molecular proportions of an aromatic pri-' maryamine with three molecular proportions of an aldehyde. Such a compound,which I have termed the aldehyde derivative of a Schiifs base, may bereacted with an additional quantity of the same or a different aldehydeto produce a modified and further reaction or condensation product whichI have termed the aldehyde reaction product of an aldehyde derivative ofa Schifis base. The compounds included in this last mentioned class areusually much harder and 2 more resinous than are the simplercondensation products and possess valuable properties as rubbervulcanizing accelerators, as I have fully described and claimed in mycoending application, Serial No. 627,327,

I) hled March 24, 1923.

The various accelerating compounds falling within the definitions ofthese two classes of substances are all of and by themselves excellentaccelerators of the rubber vulcaniz- 8! ing process. I have now furtherfound that various mixtures of these different types of more or lessclosely related compounds may with advantage be used in rubber mixes toproduce a vulcanized product which possesses peculiarly characteristicand valuable commercial qualities.

Although it is possible to use various proportions of these differenttypes of compounds in the manufacture of a vulcanized 46 rubber product,I have found that it is usually desirable to prepare a mixture in whichnot over 25%, and referably approximately.

23% of the aldehy e derivative of a Schifis base is homogeneouslyadmixed with not less 60 than 75% and preferably with approximately 77%of the aldehyde reaction product-of the aldehyde derivative of a Schiifsbase.

According to the preferred method of prea onto, a some a: non orApplication filed February 17, was. Serial no. area.

paring these various compounds, as fully described and set forth in mycopending application Serial No. 627,326 filed March 24, 1923, analdehyde, such as acetaldehyde is reacted withan aromatic primary amine,such as aniline, whereby three molecular proportions of the aldehyde arecombined with two molecular proportions of the amine. The water ofcondensation may or may not be but preferably is removed by drying untilnot more than 2% water remains in the product which may then be reactedupon 5 with an additional quantity of the same aldehyde or with anotheraldehyde, such as formaldehyde, if desired. This second reaction productmay then be dehydrated until not more than 2% water remains in the ma-7@ terial. The preparation of the second product by the further actionof an aldehyde upon the first named product is fully described andclaimed in my co-pending applirlzgggn, Serial No. 627,325 fi led March24,

The mixture of accelerators whose use I disclose and claim in my presentinvention may be readily prepared by taking approximately 77 parts ofthe second dehydrated 80 product mentioned above and carefully meltingwith it while stirring vigorously so to avoid overheating, approximately28 parts of the first mentioned dehydrated product. It is, of course,possible to mix these materials by adding the desired roportions of thenecessary ingredients w 'le either or both of the 'materials are in themolten condition, that is, upon the completion of the respectivedehydrating steps in the preparation of the materials as mentioned. Uponcooling of the mixture, the product may be readily ground and sifted tothe desired degree of fineness.

The product, when prepared in the manner as described, may beincorporated into a number of different types of rubber mixes, dependinupon the character of the final vulcanize product desired. Although thepreparation of such rubber com ounds is readily apparent to thoseskilled in the art, the following formula is given" as one in which thevery desirable properties of the above mentioned mixture of acceleratorsis readily apparent. One hundred parts of rubber of the grade known tothe trade as smoked sheets, 3.5 parts of sulfur, 5 parts of zinc oxideand 1 part of accelerator are mixed on the differential rubber mills inthe well known manner. -As an accelerator I preferably employ onecomprising approxi mately 77% of the aldehyde reaction roduct of thealdehyde derivative of a Schi s base homogeneously admixed withapproximately 23% of the aldehyde derivative of a Schifis base. Therubber mix is then vulcanized in a press under a pressure ofapproximately 40 pounds of steam per square inch for a period of about30 minutes. It is found upon test ing the vulcanized product that themodulus at 300% elongation is 347, at 500% is 626, at 700% is 2425; thetensile strength at break is 3565 pounds per square inch and theelongation at break is about 7 7 0%.- These values are indicative of thevaluable properties of a vulcanized rubber product produced byemployingmy mixture of acceleratorsand are characteristic of the entireclass of compounds. 7

As an example of the type of a Schifis base which I ma employ in thepreparation of the compound: mentioned, I prefer'to use one prepared bythe reaction of acetaldehyde upon aniline whereby ethylidene aniline 1sproduced. This compound is then reacted with a further quantity ofacetaldehyde to produce the acetaldehyde derivative of ethylideneaniline which is preferably dehydrated to a moisture content ofapproximately 2%. This compound is comparatively soft at temperatures aslow as 30 to 40 C. and in order to be. used advantageously and mostreadily in a rubber mix, is best compounded by the process known asmaster batching: Y

This additional compounding step, however, is not necessary and may beavoided if the softer material be mixed, as shown, with a harder productand as such a product I prefer to use the formaldehyde or acetaldeyde orfurther aldehyde reaction product of the softer material just mentionedwhich reaction product melts at about 80 C. My process broadly then,includes the preparation of a rubber product by employing as anaccelerator a mixture of compounds, one of which possesses a lowermelting point than the other. By this method, the master batching of thelower melting accelerator is avoided.

This method of preparing and using a mixture of two vulcanizationaccelerators as hereinbefore disclosed is also a very desirable means ofadvantageously employin an accelerator of fast curing properties. uch anaccelerator, unless skillfully compounded in theu'ubber mix, and the mixcarefully vulcanized, under Some conditions may produce or cause someundesirable effect in the rubber, such as scorching, overcuring and thelike. It is, of course, possible to vulcanize a dehyde reaction productuct as the quantity of aldehyde employed isincreased. In general, themore formaldehyde that is added to the acetaldehyde derivative ofethylidene aniline and analogous compounds, the lower will be the curingpower of the roduct formed and the higher will be the p ysicalproperties produced in the rubber compound when cured at 40 pounds ofteam pressure to the square inch.

By employing the mixture of accelerators mentioned I accomplish severalobjects. Thus, I may take advantage of the high curing power of the oneaccelerator without undue danger of scorching the rubber product andincrease the tensile strength of the product by employing the desirableproperties of a second accelerator. It is possible and entirely probablethat a rearrangement of certain of the reactive groups in the respectivecompounds may take place at the temperature and under the conditionsimposed' when mixing of the accelerators takes place but of this it isonly possible to theorize, inasmuch as the compounds themselves arehighly resinous materials of more or less unknown and as yetundetermined chemical constitution and configuration.

It is to be understood that the accelerators used in m process are notlimited solely to those produced by means of the compounds mentioned inthe example given. In place of aniline, I may employ any aromaticprimary amine, such as the xylidenes, the toludines and the like and inplace of the acetaldehyde and formaldehyde mentioned, I may use otheraliphatic aldehydes such as propionaldehyde, butylaldehyde and the likeor unsaturated aldehydes such as crotonaldehyde, acrolein, etc. It isalso understood that the examples I have given are explanatory and notlimitative of my invention which I intend to claim as broadly as theprior art permits.

What I claim is: p

1. The process of producing vulcanized rubber which comprises heatingrubber and sulfur celerators, said mixture comprising the aldeh dederivative of a 'Schiffs base and the of the aldehyde derivative of aSchitfs base.

2. The process of producing vulcanized rubber which comprises heatingrubber and in the presence of a mixture of act eater rubher whichcomprises heating rubber and 4 tion far in the resence of a mixture ofac-v celerators, sai mixture comprising 23% of the aldeh de derivativeof dehydrated ethylidene ani inc and 77% of the aldehyde reacroduct ofthe aldeh de derivative of dehy rated eylidene ani inc.

t. A. rubber product comprising the vulcanization product of rubber,-sulfur and a mixture of accelerators comprising the aldehyde derivativeof dehydrated ethylidene aniline and the aldehyde reaction product ofthe aldeh de derivative of dehydrated ethylidene 1. inc.

5. A rubber product comprisin the vulcanization product of rubber, sulurand a ture of accelerators comprising 23% of the aldeh de derivative ofdehydrated ethylidene ani he and 77% of the aldehyde reaction roduct orthe aldehyde derivative of dehy rated ethylidene aniline.

6, A rubber roduct comprising the vul- 50 canization pro not of rubber,sulfur and a mixture of accelerators comprising the aldehyde derivativeof a Schifis base and the aldehyde reaction product of the aldehydederivative of a Schrfis base.

, 7.; The recess of PI'OdllCZ vulcanized rubber which comprises heatingrubber and sulphur in the presence of a mixture of accelerators, saidmixture comprising one part of the reaction product of three molecularproportions of an aliphatic aldehyde with two molecular proportions ofan aromatic primary amine admixed with approximately three parts of theproduct resulting from the treatment with an aliphatic aldehyde of thereaction product of three molecular proportions of an aliphatic aldehydewith two molecular proportions of a primary aromatic 8. The process ofproducing vulcanized rubber which comprises heating rubber and sulphurin the presence of a mixture of accelerators, said mixture comprising aproximately 23% of the reaction product 0 three molecular proportions ofan acetaldehyde with two molecular proportions of aniline admixed withapproximately 77% of the product resulting from the treatment withformaldehyde of the reaction product of three molecular proportions ofacetaldehyde with two molecular proportions of aniline.

lln testimon whereof I it; my signature LAYTQN @LIN NGRTH.

